A variety of testing equipment may be used during the disk drive engineering and manufacturing process in order to test disk drive components in development and to verify that disk drive components are functioning properly before disk drive assembly. Such testers include dynamic electrical testers for head gimbal assemblies, fly height testers, and other testers/spin stands configured to test read channel and controller hardware/firmware.
The testing equipment described above typically includes a spindle assembly configured to spin one or more disks at high speeds. In many testers, the spindle assembly includes an air bearing spindle motor, and thus the disks may not be electrically coupled to a physical ground via the spindle motor. During testing, a head approaches one of the disks, and, since the head is physically grounded, a difference in electrical potential between the disk and the head can develop. An electrostatic discharge (“ESD”) event between the disk and head can thus occur and potentially damage or destroy the head and circuitry coupled thereto.
As a result, many testers incorporate mechanisms for equilibrating the electrical potential between the head and the disks. In some testers, a contact button electrically coupled to a physical ground is positioned at one end of a spindle shaft to which the disks are electrically coupled. The contact button rubs against the spindle shaft and provides an electrical conduit to ground.
Unfortunately, this grounding technique suffers from a number of disadvantages. First, the contact button wears out quickly, and must be frequently replaced. Second, as the contact button wears down, it may cause the spindle assembly to wobble slightly, which, in turn, can cause the head to wander off-track.
There is therefore a need for an improved mechanism for bringing the head and the disks to approximately the same electrical potential.